In the realm of broadband network communication two competing, and largely incompatible transport protocols—Asynchronous Transfer Mode (ATM) and Internet Protocol (IP)—have each developed substantial adherents among the user community, with large traffic bases deployed for each protocol. Networks using the ATM protocol are connection oriented, offer quality of service guarantees, and are generally thought to offer a slight performance advantage over IP-based networks, particularly for voice traffic. However, IP-based networks, which are connectionless, offer variable packet sizes which in some cases provides an advantage over the fixed packet size of ATM. Moreover, legacy data traffic is, in large part, based on the IP protocol.
While it is generally reasonable and practical to configure local networks for the transport of one or the other of these competing protocols, the substantial incompatibility between the two protocols creates a problem for backbone networks which may interconnect both ATM-based local networks and IP-based local networks—essentially, ATM traffic cannot by handled by an IP network and vice versa. Although it might be possible to address that problem by the construction of duplicate ATM-based and IP-based backbone networks, that is an obviously inefficient approach and would substantially increase the cost of communications over such backbone networks.
One approach to this problem, based on the assumption of an ATM-based backbone network, has been the development of methods and proposals for transmitting IP traffic over such an ATM backbone network. Among such proposals is that of the Internet Engineering Task Force (IETF) Request for Comments (RFC) 1577 and RFC 1843. Two other approaches have been developed by the ATM Forum: (1) Local Area Network Emulation (LANE) and (2) Multi-Protocol Over ATM (MPOA).
At the same time, proponents of IP-based network transport have continued to address perceived limitations in IP, relative to ATM. In particular, quality of service issues within IP networks are being addressed with proposals such as the IETF's Resource Reservation Setup Protocol (RSVP), and its proposed Differential Services and Multi-Protocol Label Switching (MPLS). Moreover, with the availability of gigabit, and in the near future, terabit, routers, both transmission latency and quality-of-service guarantees on the order of those achieved by ATM backbone networks can be met by IP networks. It is also noteworthy that major U.S. communications carriers, such as Qwest and Level 3, are implementing IP backbone networks.
Thus, given the likelihood that IP-based backbone networks will be in use for some considerable time into the future, there is a need for a means to transport ATM-based traffic via an IP-based backbone network.